The Rear Grip Thread: Ride Height, Spring Rates, Anti-Squat

[MikeE36]

On the subject of RTABs and RTAB brackets. What are all of you guys running? I have custom brackets to allow more toe in and the garagistic offset bushings. But it seems I may need to go to a bearing style RTAB to allow proper movement of the trailing arm under compression.

And also. What are you guys running for rear toe? I'm at about .25 degrees toe in on each side.

Interested in these offset bushings - link?

I run turner motorsport RTAB bearings, with some custom brackets to allow more toe in. I'm at 0.25" in per side, 0.50" total. I don't know in degrees. More toe in = more bite in my experience, but at the expense of tire wear sometimes. Lately though with the higher ride height and more anti-squat, the car doesn't change camber so much on throttle, so the tire actually seems to wear much more evenly than before, despite the only change being increasing the ride height really.

Mike

[jakermac]

Justin is at irwindale, convince him to go measure that distance in kristaps' car haha. Although I think he has wisefab rear knuckles so that probably drops the point where the trailing arm mounts anyways

Interested in knowing more about this. Can anyone point the way? Dont see anything on Wisefab's site about them.

[RandomHero27]

nerptech makes the offset rtabs that allow for the toe correction. http://nerptech.bigcartel.com/produc...inserts-rtab-s

instagram user makemeritchbitch makes the offset brackets.

[Jrcanes55]

Interested in these offset bushings - link?

I run turner motorsport RTAB bearings, with some custom brackets to allow more toe in. I'm at 0.25" in per side, 0.50" total. I don't know in degrees. More toe in = more bite in my experience, but at the expense of tire wear sometimes. Lately though with the higher ride height and more anti-squat, the car doesn't change camber so much on throttle, so the tire actually seems to wear much more evenly than before, despite the only change being increasing the ride height
Mike

https://store.garagistic.com/bmw-per...g-arm-bushings
Delrin bushings. They're not the best. I'm going to most likely switch to the nerptech offset bearings.

nerptech makes the offset rtabs that allow for the toe correction. http://nerptech.bigcartel.com/produc...inserts-rtab-s

instagram user makemeritchbitch makes the offset brackets.

I actually have driftec brackets. The brackets that dude makes are for stance cars. The ones I have we specifically designed to give as much toe in as humanly possible.

And another note. I have noticed a huge difference in tire wear with toe in. I was destroying tires at one of our local events and had to back it out a bit.

[RandomHero27]

https://store.garagistic.com/bmw-per...g-arm-bushings
Delrin bushings. They're not the best. I'm going to most likely switch to the nerptech offset bearings.




I actually have driftec brackets. The brackets that dude makes are for stance cars. The ones I have we specifically designed to give as much toe in as humanly possible.

And another note. I have noticed a huge difference in tire wear with toe in. I was destroying tires at one of our local events and had to back it out a bit.

you wouldnth happen to have a link for the brackets would you? the only ones i know of are by the instagram user? i goggled and cant seem to find the driftec brackets.

[tptrsn]

Whoa, I didn't know nerptech had the spherical RTABs, let alone in the offset variety at a pretty reasonable price!! Wish I had known that before I got urethane RTABs.

[tptrsn]

And another note. I have noticed a huge difference in tire wear with toe in. I was destroying tires at one of our local events and had to back it out a bit.

Are you saying that too much toe-in was adding a lot to your rear tire wear?

[protomor]

I'm new to this type of rear suspension. Can someone refresh my memory? Lowering an e36/e46 creates toe out. So these offset rtabs toe in to get you back closer to stock? Or are we trying to get to 0?

I suppose it's impossible to raise the rtab the same amount as your subframe and maintain perfect factory geometry?

[Mikestokman]

Lowering causes excessive toe in, so you notch the bracket to allow you to move the bearing/bushing itself outward more. Bearings are way sicker than bushings btw, my car feels better than it ever has.

[tptrsn]

Lowering causes excessive toe in, so you notch the bracket to allow you to move the bearing/bushing itself outward more. Bearings are way sicker than bushings btw, my car feels better than it ever has.

Did you make yours? If so, how did they turn out?

[protomor]

Right? So why is everyone talking about getting more toe in?

[welchct]

Any of you guys contemplated ditching the IRS all together? I have been playing with the idea in my head a lot lately. A simple 4 linked solid axle seems like it would be so much easier to tune. Plus the parts to build what I want are a ton cheaper. I have several options that would cheaply go under my car sitting here too, so that's a lot of my own personal appeal.

It's not like the stock radius arms are a fantastic design or anything. Lol

[tptrsn]

Damn dude, you are a heretic. I LOVE IT!!

Actually, I have been looking at lots of different options for slapping a narrowed (on one side) 8.8 under my s#1tbox, maybe over the winter... I'm thinking of everything from a 4-link, to a 3-link, to a torque arm, with a panhard bar or a watts link, or even some ridiculous leaf springs for a trailer with some caltracs. Lol

So what do you think would package best?

[welchct]

Hahaha. That's been the story of my life. In this case probably has everything to do with my background though. Grew up in a winged sprint race team. Graduated to building rock crawlers for a living. I'm by no means a BMW guy. I just bought what was cheap and easy. So I'm starting from way outside the box.

I'm very well versed in setting up a solid axle suspension. I'm not nearly as confident in the radius arm IRS systems. What does piss me off, as a shop who builds lots of diffs, is the complete lack of aftermarket support for these BMW diffs. It's absurd what companies want for traction devices and gear set's.

I'm running Jeep wheels on my car already. They're a 5x5bp. Sadly, the JK rears with that pattern are a bit too wide. I think something around 60" wms/wms would be great. Thus, your 8.8 explorer diff would be perfect. There's no reason to even narrow it... at least in a e46. Not sure how it'd fit a e36. I already have a built dana 44 on the rack with a full spool, 4.56 gears, and 4340 axle shafts. It's disk brake too. It would be your typical TJ/YJ/XJ axle. It has a WMS of 60.5". Which would be perfect. I could run 1.5" wheel adapters to go from 5x4.5 (114.3) to 5x5 for my wheels and still clear my wheel arches in the back. I like the non c-clip aspect and cheaper parts the dana axles offer over the 8.8. A 9" would be my second choise. Plenty of axles out there would work.

I would build a parallel 4 link. Use 3/4 heims for the links. 3/4 to 1/2 misalignment spacers. 1.25x.120 DOM tube with weld in bungs for the links. A long panhard would work fine as long as you keep it flat.

Link mounts and panhard mounts can all be built with multiple locating holes in .75" increments at both the axle side and frame side.

Continue using 2.5" coilover coils in the factory spot. Swap to closed loop top shock mounts. Then any rebuildable emultion or reservoir shock could be used and then tuned. You could even valve several sets for different track conditions.

Drive shaft could be a simple u-joint shaft with a spline mid slip like I'm building in my other thread.

Move to a fuel cell and reinforce the bulk head at the rear seat to hang the link mounts.

Then, if you don't know how to design or tune a proper 4 link system, you can use the 4 link calculator to play around with how certain adjusts effect figures.

[XLS] 4 Bar Linkage Calculator v3.0 - www.patooyee.com!
www.patooyee.com › 4BarLinkV3.0c.xls

I honestly think I could do it, and tune it for less than $300. But like I said, I have most of the stuff here already. I even have some 3.07 gears and several different types of limited slips on the shelf. I'm kinda liking the idea of adding an electric locker to it too. For less than $1000 you can have a push button spool and a clutch style limited slip when off. Or just do a truetrac for $500 or less.

Personally, I think it's a worthwhile endeavor to try. It just comes down to my desire to fix what isn't broke yet.

[MikeE36]

Lowering causes excessive toe in, so you notch the bracket to allow you to move the bearing/bushing itself outward more. Bearings are way sicker than bushings btw, my car feels better than it ever has.

Lowering excessively causes toe-out. At a really low ride height, I had to modify my RTAB brackets to allow more toe-in.

Any of you guys contemplated ditching the IRS all together? I have been playing with the idea in my head a lot lately. A simple 4 linked solid axle seems like it would be so much easier to tune. Plus the parts to build what I want are a ton cheaper. I have several options that would cheaply go under my car sitting here too, so that's a lot of my own personal appeal.

It's not like the stock radius arms are a fantastic design or anything. Lol

I'm sure it would work better with a true tuned 4 link back there, but realistically we're all a bunch of broke drifters that don't want to fab all that much stuff up, or don't have the know how. Also, changing the rear suspension that dramatically makes it illegal for Formula Drift, which isn't a huge concern here but is still something to consider.

Mike

[welchct]

I yeah, Formula D rule book means nothing to me. It's really silly that anyone outside of pro teams even follows it. I can't really even believe drivers own their own cars at that level anymore. Lol

I posted a link to the 4 link calculator. That's a great tool to better understand how geometry changes effect things like anti-squat and roll center or center.

[tptrsn]

Maybe it would be better to start another thread rather than mess up Mike's thread that has a rather specific intent. I'm interested in knowing if you have any ideas of how to setup the best solid axle link set that would keep the factory fuel tank (assuming E46 is basically like E36 in that regard).

[welchct]

You would need to remove the factory tank to have proper link geometry with a solid axle rear.

[tptrsn]

Even with a 3-link? Should work with a torque arm for sure instead of a 3-link, shouldn't it?

[welchct]

In my opinion, yes. It's in the way of where the lowers should go. They really do need to be pretty long. That's the biggest issue guys make when building a 3 or 4 link. Suspension travel effects anti-squat in huge ways with short control arms. They make radical angle changes through their travel. It can even cause the whole axle to steer if the suspension is articulated like it would be under body roll conditions.

[protomor]

There's a reason no one uses solid axles in pro drifting. And why JR ditched it as soon as he could. But then again, JR's team really likes that 3 wheeling thing for some reason.

IMO the rear grip debate is pretty simple. Do your best to lower CG but maintain factory roll geometry. IE keeping your roll center close to the CG. Which just means you raise your subframe and all subsequent external attachments the same effective amount (as possible) as you lower the car.

Well the idea is simple. Execution is difficult. On E30s, it's raise the rear subframe and adjust out whatever else you can. On E46/E36s, its the same but raising the trailing arm to chassis mounting point too. The front is a whole other debate however.

[Novablue454]

Raising the rear subframe is illegal per FD rules.

- - - Updated - - -

Right? So why is everyone talking about getting more toe in?

I run 1/4" toe in, I thought that was pretty standard?

[protomor]

Raising the subframe past a certain amount is illegal in FD. But also solid rear is much more illegal.

I thought people ran toe in when they didn't have spherical bushings to make up for deflection on throttle. If you have spherical RTABs, wouldn't you want closer to 0 rear toe?

I've been out of this thought process for a while so I think my memory is playing tricks.

[MikeE36]

I yeah, Formula D rule book means nothing to me. It's really silly that anyone outside of pro teams even follows it. I can't really even believe drivers own their own cars at that level anymore. Lol

I posted a link to the 4 link calculator. That's a great tool to better understand how geometry changes effect things like anti-squat and roll center or center.

Some of the pro-am / grassroots series across the US require drivers to follow the full FD rulebook to the T, so that stuff becomes relevant pretty quickly. In Texas, our series isn't quite as strict so it's not as big of a deal. I can guarantee you I would receive a crapload of protests though with a 4 link setup under the rear once everyone figures out what is going on.

Mike

[Jrcanes55]

you wouldnth happen to have a link for the brackets would you? the only ones i know of are by the instagram user? i goggled and cant seem to find the driftec brackets.

There is not link to the bracket unfortunately. "Driftec" is just what we call my friend. He makes a few s13 things on the side and was nice enough to come measure my brackets, draw up a design in solidworks, and then have a set produced. He still has the designs. If anyone is interested in brackets I could possibly see about a group buy. Mine are the first and only set and we've decided to make a few changes to them if there was enough interest in producing them.
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